Because present day building materials are required to be resistant to both fire and mold, woodfiber board and chipboard is being replaced to an ever increasing extent with primarily plasterboard (gypsum).
Several methods and devices for fastening electric cables, paintings etc., to porous support surfaces, such as plasterboard panels, or for suspending devices on such surfaces are known to the art. Those methods which afford the most reliable attachment are based on the use of attachment devices comprising fasteners which pass through the panels, or on the use of special duty plaster screws or plugs. One drawback with such attachment devices is that they are difficult and time consuming to attach. Furthermore, such devices are relatively expensive. The quickest way of securing articles to such porous support surfaces is to use, inter alia, conventional attachment and suspension devices, such as nail clamps and X-hooks. Although these attachment devices are able to take up transversely acting loads in an acceptable manner, they are less than satisfactory with regard to taking up loads which act in a fastener-withdrawing direction. In order to obtain reliable attachment to the best possible extent when using attachment devices of this kind, it is desirable to locate the attachment devices in positions in which the fasteners used therewith will enter into an underlying stud or nogging-piece. When the articles to be attached in this way are electric cables, it is found necessary in some cases to extend the cables farther than would otherwise be required and, moreover, often in a manner which is less pleasing from an aesthetic point of view.
In order to enhance the ability of conventional attachment and suspension devices to take up such fastener-withdrawing forces satisfactorily, it has been proposed to skew-nail such devices to the support material, skew-nailing being a method in which nails are driven into the support material while inclined thereto. When skew-nailing, there has been used either two separate nails or a U-shaped fastener whose legs are caused to diverge or converge through the action of guides provided in the attachment device and/or are formed at their extremities in a manner which will ensure that the legs converge or diverge when driven into said support material. Both of these variants are disclosed in the German Offenlegungsschrift No. DE 3115914 A1, for example FIG. 9 of this publication illustrates an attachment device which is secured with the aid of two nails, whereas FIGS. 3 and 5 of the publication illustrate an attachment device which is fastened with the aid of a U-shaped fastener, this fastener being shown separately in FIG. 6.
Both of these fastener types have the drawback of relaxing their grip slightly when subjected to relatively small withdrawing forces, such that the attaching device will no longer abut the support surface. This is due to the fact that the bearing surface of the fastener means which takes up the withdrawing forces is relatively small in area, and consequently the surface pressure thereon becomes so high as to crush the underlying brittle support material. As the attachment device moves, this crushed material becomes packed forwardly of the fastener means in the withdrawing direction thereof and forms cushions or crushed-zones which are able to withstand the withdrawing forces to a greater extent than the unaffected material and therewith prevent continued withdrawal of the fastener means used to fasten the attachment device. When these withdrawing forces cease, the attachment device will return, either partially or fully, to its original position. Furthermore, the crushed material in the fastener holes of the attachment device is often redistributed so that upon the reoccurrence of such withdrawing forces further material is crushed. Should these withdrawing forces be repeated intermittently, the fastener means will gradually work out of the support surface and the attachment will become progressively looser, until it falls away. These intermittently occurring forces which tend to withdraw the fasteners may be caused as a result of cleaning or dusting externally fitted cables of various kinds, for example. When the attachment device is used to hang paintings, pictures, or mirrors in the vicinity of doors, such withdrawing forces may occur intermittently as a result of closing the door. For example, the surges of air generated when closing the door are liable to cause the painting, etc., to rock and thereby subject the fasteners to withdrawing forces.